The effect of dietary undernutrition (caloric restriction) on lifespan, disease pattern and immune response will be assessed further, including populations of mice in which different diets during the growing period and during the adult and late-life times are instituted. Immune function will be measured in these new populations by mixed lymphocyte reaction, response to sheep red blood cells, response to mitogens, by cell-mediated lymphocytotoxicity, and by response to TNP-labeled syngeneic mouse lymphocytes. Further studies of immune functional changes in normal aging mice will also be undertaken using the above tests. The level and types of suppressor cells in the dietarily restricted and normal mouse populations will also be investigated. BIBLIOGRAPHIC REFERENCES: Naor, D., Bonavida, B., and Walford, R.L.: Autoimmunity and Aging: the age-related response of mice of a long-lived strain to trinitrophenylated syngeneic mouse red blood cells. J. Immunol. 117:2204-2208, 1976.